Hydrofluoric acid product and method of producing the same



H. B. BISHOP July 27,1937.

HYDROFLUORIC ACID PRODUCT AND METHOD OF PRODUCING THE SAME Filed July 50, 1952 2 Sheets-Sheet 1 INVENTOR flow/sms B) SHO? BY /M MMA MM ATTORNEYS www July 27, 1937. H. B. BISHOP 2,088,048

HYDROFLUORIC ACID PRODUCT AND METHOD OF PRODUCING THE SAME Filed July 50, 1932 2 Sheets-Sheet 2 -s a s i Q ox l\ l f\ d I I 'e PLI .a l 11 b 'Aq :i n f2 b l 1 Q l il \' Ny m E: LA

INVENTOR HOWARD 3.515507 ATTORNEYS Patented July 27, 1937 UNITED STATES PATENT OFFICE HYDROFLUOBC ACID PRODUCT AND 15 Claims.

The present invention relates to a hydroiluoric acid product and method of producing the same. 'Ihe product in question differs from chemically pure anhydrous hydrofiuoric acid in that it is a rectification product and comprises, besides HF a minor percentage (of the order of less than 3% and preferably less than 116 of 1%) of alien substances such as water, silicon tetra-uoride and iron, all of them indigenous to the raw material or the apparatus used for rectication but inactive in their own respective capacities in the state of extreme dilution in which they exist in the product.

Heretofore hydrouoric acid has been made in 15 the laboratory by heating anhydrous potassium bi-uoride and condensing the vapors. In this way a 100% HFproduct may be obtained but the process is so expensive as not to be avaliable for Other processes for prof` commercial purposes. ducing concentrated HF, heretofore proposed, involved distilllng a concentrated acid solution and absorbing the acid vapors therefrom in concen-4 trated acid, in this way increasing the concentration to a solution containing about 85% to 90% HF. Another method heretofore proposed comprises fractionally condensing at decreasing temperatures the gases evolved from heating aqueous solutions of hydrofiuoric acid and then to render the product anhydrous by treating with oleum. This method proved impractical because the hydrofluoric acid forms an addition product with sulphuric acid or oleum with generation of considerable heat and it is practically impossible to effect a separation when thus combined.

Commercial anhydrous hydrouoric acid has therefore thus far been an unknown commodity, incapable of production by any known procedure. Y I have now discovered that important and valuable results may be obtained in the industry by 40 retraining from the eiort to produce chemically pure anhydrous hydrciiuoric acid or from striving to get along with concentrated solutions of hydrofiuoric acid containing up to 90% HF but in lieu thereof producing a product which shall be sub- 45 stantially anhydrous hydrofluoric acid stlllcontainhowever alien substances indigenous to the raw material or the apparatus used for rectification, provided that the percentage cf the vaggregate amount thereof is reduced to such a minor degree as to render them inactive in their own respective capacities, i. e., below 3% and preferably less than 115 or 1%. Such a product is wholly new and was never, so far as I am aware, produced before my invention thereof. In order to produce the new 65 product, I have devised suitable apparatus and methods capable of arriving at the desired result.

The method, brieiiy stated, comprises conducting the reaction product of sulphuric acid and calcium iiuoride through a scrubber preferably containing crushed and graded fluor-spar, cooling 5 the gas which has passed through said scrubber to a temperature such that a maximum vapor pressure ci HF and a minimum vapor pressure of water is obtained. using the condensate of said cooling step to flush out the scrubber, compressing the gas which was not condensed in the cooler, and then condensing the gas under the said pressure. The pressure step, being an aid to the liquefaction of the hydrofluoric acid, may, of course, where facilities are available, be replaced by more intense refrigeration. Preferably a purification system for the elimination of the sulphur impurities, solids, scale, oil from the compressor, and the like, is interposed between the preliminarycooling stage and the condensing and reirigerating stage. Preferably, also, the drip acid which has been used for flushing the scrubber is utilized in conjunction with an absorbing system for the residual gases from the refrigerating system. whereupon a fractionatins procedure may be advantageously applied tothe result to supply additional quantities of the substantially anhydrous HF.

Apparatus suitable for carrying out the invention is illustrated in the accompanying drawings 30 which are illustrative of one form of apparatus which may be advantageously employed to perform the improved process and to produce the improved product. Fig. 1 is a diagrammatic view of the apparatus through to the refrigeration stage, and Fig. 2 is an. extension or continuation of Fig. 1 showing the apparatus lying beyond the point where the product is refrigerated. The two figures together represent a single set of apparatus divided for purposes of presenting larger scale drawing than would be possible if the whole of the apparatus were shown on a single sheet.

In the drawings the line I indicates a conduit pipe leading from a still or reaction vessel, constructed in a weil known manner, in which ves- 45 sel a high boiling acid. e. g.. concentrated sulfuric acid, is caused to react upon a uoride, such as calcium fluoride, the latter commonly called iluorspar, at a temperature of about 600- 800 F., whereby hydrofluoric acid gases are gen- 50 erated which contain a small amount of sulfuric acid vapors and also entrained droplets of such acid carried over by the gas stream, sulfur dioxide, sulfur trioxide, water vapors, volatile silicon compounds. dust particles and traces of other 55 impurities. These gases are under the influence of the sucking action generated by the working of. the compressor pump 21.

-It is advantageous to have the gases from the still as free from air as practicable in order to screen 3 is suitably arranged upon whichla layer of a scrubbing material t, capable of reacting with sulfuric acid, is provided. As filtering means iuorspar is vused on account .of its ability not only toreact with the rsulfuric acid but also to form additional hydroiiuoric acid gas by. this reaction and an insoluble, readily removable sulfate, calcium sulfate. The scrubbing material is arranged upon the screen in such a way that the gases rst have to pass coarse particles of the scrubbing medium which gradually become smaller and smaller, the size of them varying v from 2 inches diameter at the bottom to l/2 inch 35 being discharged through pipe 2d as drip acid int` a suitable drip acid storage tank 22. 'I'his drip' acid, when passing the lter bed t, washes down diameter at the top of the filter bed.

After passing the scrubber 2 the gases are conducted through pipe 5, connected to the upperpart of the scrubber 2 preferably at a point diametrically opposite to the point of connection of the pipe I, to the cooler 6 of any suitable constructiom e. g., comprising anv interconnected .pipe system which iscooled by a stream of water to about 70 F., the water being supplied bythe water pipe line 1 'and drawn oil' by the-trough 8. In the cooler 6 the HF gas and the condensed water containing HF are brought to a temperature equilibrium, the temperature being such that a maximum vapor pressure of and. a minimum pressure of water'isobtained. In'v other words, the HF gas is used as its own drying agent, avoiding entirely the necessity of adding any foreign drying medium such as sulfuric acid. The condensed and uncondensed components of the gas and vapor mixture ow into the separator 9 wherein lthe condensate, consisting ofhydrouoric acid and condensed water vapor, is separated from the gas and is drawn off through a pipe Il provided with a suitable trap I0. This pipe Il is connected with the scrubber 2 and terminates in a distributor I2 arranged at the top of the scrubber 2. In this Way the condensate is distributed upon the-upwardly flowing gases after they have passed the lter bed 4 where they have been freed from sulfuric compounds. The Warm gases thereby drive out a portion of the Jhydrofluoric'acid contained in the condensate,

the remainder trickling through the filter bed 42,'

flowing toward the bottom of the scrubber 2 and the calcium sulfate formed by the reaction-ofthe gas-vapor mixture with the absorbing medium. It has a concentration of about 60-'70% hydroiiuoric acid. The acid from thetank 22 may be periodically recircul-ated through the scrubbingtower 2 to Wash down the calcium sulfate in which case the acid for that purpose is taken from the line 1I` at IIa. A

The uorspar of the iilter bed t is replaced from time to time.

At 23 the drip acid storage tank is connected with a pipe line 1I by which'the drip acid is conveyed to the' feed tank 13 and to the fractionating still 11 as will be described later on.

'Ihe uncondensed gases leaving the separator 9 are conducted to the fog eliminator It by the pipe line I3. 'I'his fog eliminator has-ascreen I8 arranged in it upon which a layer of charcoal I5 or any other suitable material capable of removing sulfur trioxide fume and other solid and liquid bodies carried along by the gas stream is provided. After leaving the fog eliminator It at I'I and passing through the pipe 25 and a separator 26 (to prevent scale from the pipe lines or other foreign solid matter passing into the compressor) the gases are sucked into the horizontal compressor 21, preferably one which is equipped withpoppet valves and having'the inlet valves in the top' and the discharge valves in the bottom of the compressor. By the action of this compressor the gas is compressed to a pressure of about 60 lbs. 'I'he compressed gas', after passing the oil separator 28 wherein entrained oil from the compressor is separated and drained ofi, is then conducted by the pipe 29 to the top opening 3l of the condenser 30 constructed in any suitable manner wherein the gas is cooled below the boiling point of the hyd-rofluoric acid, i. e., t0 atleast 50-60 F. The c00ling is accomplished by a stream of cold water entering the condenser at 33, and leaving it at 32. outlet water may be used to supply `the -water vfor the water line 1, in which case the connection 32a is made use of. In this condenser part of the hydrouoric acid is liqueiied.- It leaves t0- gether with the uncondensed gas the cooler atv 36 through the pipe 35 which is connected with the T-pipe 36 from where the uncondensed gas flows through the pipe line 31 into the second cooling system. The condensed hydrouoric acid is discharged into the receiver tank 33. It it here under the influence of the pressure ofthe uncondensed gas and is periodically dischargedthrough the pipe line 39 through valve 3|' into the weighing bottle 4I placed upon the scale 42. The gas pressure forces the liquid hydrouoric acid into the weighing bottle III. When the valve 39 is closed the liquid hydrofluoric acid again begins to accumulatein the receiver tank 38 while the uncondensed gas. as described before, flows into the preliminary cooler 40 of the second low temperature cooling system which it enters through line 31.

This second cooling system consists of a tank divided by the partition 45 into two parts, an upper one, the preliminary cooler t0, and a lower one, the refrigerator 40. Both compartments t@ and t0' are lled with brine. 'I'he lower compartment. t0 contains a coil connected with the pipes d2 and 63, leading to and from the refrig-s erating machine t4 through which pipes and coil the vrefrigerating vliquid (sulfur dioxide or 'the like) circulates and cools the brine solution of the lower part of the tank to about 15 F. The refrigerating coil is arranged in such a way that it'supplies the refrigerating liquid in counteri current to the flow of the gas to be cooled, as can be seen in the drawings. The gases entering the preliminary cooler d0 and leaving the refrigerat-l ing part d0 at t6 are reconducted by the T-pipe 61 into the preliminary cooler d0. By the expan sion valve i8 the pressure of the cold exit gases is reduced to about 10 lbs. producing arfrlg-i erating eiect whereby the uncondensed gases coming in through pipe 3l are pre-cooled before entering the refrlgeratlng unit 40. The low tem- Thesecond majo Dart 0f the apparatus which" perature generated by this expansion furthermore, serves for cooling the brine in the upper part of the second cooling system, thev preliminary cooler. The remaining, uncondensed gases iiow through the preliminary cooler Ml in countercurrent to the inowing gases and leave it at 49.

The condensed hydrouoric acid, obtained in the refrigerating part BU' ows through the T- pipe Q1 into the receiver tank 50 from where it ls periodically discharged by the pipe line 52 provided with the valve 5|, into the weighing bottle di in the same way as described previously.

will be described in the following paragraphs, deals with the recovery of all of the hydroiiuoric acid gas which has not been condensed and recovered as liquid hydrofluoric acid in the cooling systems described above; it is of not less importance than the rst part of this process because it enables one to recover practically all of the hydrouoric acid produced by the interaction of sulfuric acid and a fluoride and renders the process very economical.

The expanded gases leaving the second cooling system at 49 are conducted by means of the pipe 53, preferably provided with a check valve (not shown), into the steel absorber 5d which is filled with hydrofluoric acid of about strength.

The gases, still under pressure, enter the absorber by means of a perforated pipe 55 or coil or any other device enabling thoroughly mixing of gas and absorption liquid.

When the acid in the absorber 5t is concentrated to about 80% strength, part of it is withdrawn through valve 5l and line 58 into the,

feed tank 'i3 from where it is charged into the fractionating apparatus 'll as will be described later on. The withdrawn acid is replaced with diluted acid-of about @45% strength in order again to reduce the strength of the acid in the absorber to about 60%. This diluted acid is supplied either from the rubber lined feed tank 63 or from the nal absorber 65 by means of the pipe lines d@ and t i, respectively, and the T-pipe 5t with suitably arranged valves. The feed tank t3 is periodically supplied through the pipe line di with 35% acid from the boiling tank l2. This acid when used for filling tank $3 is iirst cooled as for example by circulating a cooling medium through the coil 'i9 in tank 18. The gases leaving the absorber t through the pipe 62, provided with a valve 59, are freed .of the la'st amounts of hydrouoric acid in the rubber lined absorber 65 which is illed` with waterby means of the water line lil. The gases entering the tank SS through the perforated pipe 66 or coil or any other suitable device enabling intimate contact of absorption liquid and gases to be absorbed, are washed thoroughly and the residue is discharged into the air by thepipe S9. The residual gases are preferably passed through a rubber lined coke tower (not shown) before leaving the system as exhaust gases. f l

As soon as the dissolved hydrofluoric acid has reached a. concentration of about 30% in the absorber 55, it is withdrawn through the pipe 6I, provided with a valve B8, and is used for the dilution oi' the absorbing liquid in the absorber 5t. The final absorber 65 is then refilled with water. l

The feed tank 'i3 not only is filled with the acid of 80% strength from the absorber 54 but also with the drip acid of 60 to 70% strength of the drip acid tank 22 which acid is withdrawn from the drip acid tank at 23 and conducted by means of the pipe line 1|- into the feed tank 'i3 entering the latter at 12.

From the feed tank 13 thehydroiiuoric acid either may be put to commercial use as such, in which case it is withdrawn at It or it may be fractionated and returned via pipe line 9| into the system 6, I3, l5, 2l, 29, 30, 38, 4I, this proeedure resulting in an increased production of anhydrous hydrouoric acid at 4 l. For this purpose it is discharged from the feed tank 13 at 'l5 through the pipe line El and enters the fractionating column 'l1 at i6, said column being located above the boiling tank 18, heated by means of the steam coils 19.

The fractionated vapors and gases leave the fractionatlng column at 82, and are conducted by means of the pipe 83 into the cooler 84, where the temperature is reduced by water supplied by the water pipe line 85. The condensate and the uncondensed gases enter the separator 88 at86, where the condensate is returned through a trap device 89-into the fractionating column l1 at Bil.

The uncondensed gases leave the separator at 8l and are returned by the pipe line 9| to the gas mixture generated by interaction of sulfuric acid and a fluoride, preferably at 92 between the fluorspar scrubber 2 andthe rst cooler 6.

'I'he hydroiluorlc acid of 35% strength ac-f cumulated in the bottom of the boiling tank i8 is periodically discharged at 80 and transferred to the feed tank 63 by means of the pipe line 8l. It serves for replenishing and diluting the absorption liquid in the main absorbing tank 54.

It will be understood that many variations in the process as well as inthe apparatus may be made without departing from the principle of the invention as dened in the following claims. It is aiso of advantage in the ciiicient and economical operation of the apparatus that the process is a continuous one with the results produced readily controllable by regulating the operating conditions.

This improved process has in practice produced high yields of anhydrous hydrofluoric acid of a very high percentage without the aid of a drying agent other than the hydrouoric acid itself. It has been found that acid .of this degree of purity has very little, if any, eifect on iron and can therefore be stored and shipped in ordinary welded steel tanks, the welds being preferably electrically made and as free from oxide as possible as the latteris dissolved by hydrouoric acid. It has further been found that bronze is more resistant to hydrouoric acid than iron, and for such parts as valves, compressor cylinder, piston, and the like, this material preferably is used.

Dry lubricating oil is scarcely aiected, if at all, by the acid, so that good' lubrication for the compressor can be obtained. To avoid loss of gas through the stuiiing box of the compressor preferably an elongated stuing box is used.

One of the advantages of this process is that by the use of a positive compressor the gases are sucked from the still `at a reduced pressure, so that the time required to inish a charge in the still is reduced.

Furthermore, much less Water is required to cool the hydrofluoric acid gases than is required exclude the use of other suitable materials which' can be used for these purposes. i

The obtained anhydrous hydrouoric acid is especially useful for the manufacture of difluoro dichloro methane and other similar products used for mechanical refrigeration; but it may be used for any other purpose for which a substantially anhydrous and pure hydroiluoric acid is employed.

The anhydrous product obtained by the process hereinabove described consists in the :main4 of m' Vbut 'contains also minute quantities of iron from the pipe lines, avery minor per- 'centage of water and a small amount of silicon tetra-fluoride which is only minutely soluble in the hydrofluoric acid as produced by this proc,- ess. The percentage of such alienmaterials can be kept as low as .07% or even lower by the proper conduct of the processthough the percentage even when somewhat greater,4 say 3%, still leaves the product capable of advantageous use for many industrial purposes. In other words, the hydroiluoric acid product of this invention is one whose perfomance in practical use is equal to that of chemically `pure anhydrous hydroiluorlc acid notwithstanding the fact that alien substances are present to the limited degree indicated. It has also been discovered in respect/to the new product that by 'the addition of anhydrous ammonia, say 5 to 10% by weight, its vapor pressure and fuming properties are reduced to such an extent that `it can be handled in the vsaine manner as and with less annoyance than ordinary commercial 60% hydrouoric acid. Otherwise the anhydrous acid would have to be handled in steel containers made to withstand pressure, ordinarily about 15 pounds per square inch at ordinary summer temperature. combined with anhydrous ammonia, as stated, the resultant product is capable of use for the manufacture of frosting compound, for laundry purposes and other uses.

The addition 'of anhydrous ammonia to anhydrous hydrouoric acid appears toY produce more than merely a mixture of the two substances. evidenced not merely by the fall in the'vapor pressure of the hydrouoric acid, but by the large quantities of heat that -pound of the general formula (NH3) (HF) n, the

value 'of the number n being unknown and probably being variable.

It will observed that the arrangement of apparatus described permits the process to be readily adapted to varying conditions, for example, in case the gas mixture entering the apparatus at I! or the pipe 5 contains very little water, the cooling stage at 6 and l need not tze-immediately fol- "lowed by a separation of-condensed liquid in 9,

since in View of the small amount of water in me gas, it may-be left in and condensed with the c -v y 1 When bulk of the anhydrous acid. In other words, although in that case there will be a separation between the condensed liquid and uncondensed hydrouoric gas, the separation will occur at a later stage than that indicated in the drawings at S, the residual uncondensed gas in either event passing through an absorbing medium such as 56, the

liquid produced in said step being capable of further treatment by being fed into the fractionatng column il and the substantially pure anhydrous hydrofluoric acid gas separated therein from water, sulfuric and other impurities.

I claim:

1. 'The process of producing substantially pure anhydrous hydroiluoric acid which comprises subjecting uorspar to the action of a high boiling acid and maintaining in the Vexpelled gas stream a proportion of HF in excess of that which is capable of being condensed out in the form of a water solution of said acid, bringing the mix` ture of gases and vapors thereby produced in contact wtih a substance capable of reacting with at least part of the impurities contained in said mixture, separatingaqueous hydroiiuoric acid contained in the gas mixture, by cooling, bringing the condensed liquid and the uncondensed HF gas to a temperature equilibrium and separating the liquid from the gas.

2. The process set forth in claim 1, in which the condensed liquid is distributed prior to the cooling step into the stream of the gas mixture and in contact with the substance capable of reacting with part of the impurities contained in the mixture.

3. The process of `producing substantially pure anhydrous hydrofluoric acid which comprises subjecting uorspar to the action of sulfuric acid and maintaining in the expelled gas stream a. proportion of HF in excess of that which is capable-of being condensed out in :the form of a water solution of said acid, bringing the mixture of gases and vapors thereby produced in contact with relatively coarse, crushed, graded calcium fluoride, separating aqueous hydrouoric acid contained in the gas mixture, by cooling, bringing the condensed liquid and the uncondensed HF gas to a temperature equilibrium and separating the liquid from the gas.

4. The process of producing substantially pure anhydrous hydrouoric acid which comprises subjecting uorspm to the action of sulfuric acid and maintaining in the expelled gas stream a propor- `'tion of HF in excess of that which is capable of being condensed out in the form` of a water solution of said acid, separating aqueous hydrqgudric acid contained in the gas mixture thereby produced, by cooling, bringing the condensed liquid and the uncondensed HF gas to a temperature equilibrium, separating the liquid from the gas, compressing the gas, cooling the gas sumciently to liquefy a part thereof, releasing the pressure on the lmliqueed gas and employing the resultant temperature reduction in the said cooling step.

5. The process of producing substantially pure anhydrous hydrouoric acid which comprises subjecting uorspar to the action of sulfuric acid` condensed HF gas to a temperature equilibrium,

separating the liquid from the gas, subjecting the accanita gas to condensing conditions, passing the residual uncondensed gas through an absorbing medium and fractionating the absorbing medium.

6. The process of producing substantially pure anhydrousl hydrofluoric acid which comprises subjecting iiuorspar to the action of sulfuric acid and maintaining in the expelled gas stream a proportion of HF in excess of that which is capable of being condensed out in the form of a water solution oi said acid, separating aqueous hydroiluoric acid contained in the gas mixture thereby produced, by cooling, bringing the condensed liquid andthe uncondensed HF gas to a temperature equilibrium, separating the liquid from the gas, refrigerating the gas to reduce it to liquid form, passing the residual uncondensed gas i through an absorbing medium, fractionating the absorbing medium, and admixing the gas from the Iractionating step with the gas mixture on its way to the ilrst cooling step of the process.

7. The process of producing substantially pure anhydrous hydrouoric acid which comprises subiecting uorspar to the action of sulfuric acid and maintaining in the expelled gas stream a proportion of m in excess of that which'is capable of being condensed out in the form of a water solution of said acid, bringing the mixture of gases and vapors thereby produced in contact with a substance capable of reacting with at least part of the impurities contained; in said mixture, separating aqueous hydroiluoric acid contained in the gasmixture, by cooling, bringing the condensed liquid and the uncondensed HF gas to a temperature equilibrium, separating the liquid from the gas, refrigerating the gas to condense HF therefrom, absorbing the residual uncondensed gas in an absorbing medium, adding to the absorbing medium after it has become strengthened in HF content, the drip acid from that stage oi' the process where the liquid from the rst cooling step or the process is contacted with a substance capable ci reacting with part of the impurities contained in the initial gas mixture and iractionating the resultant liquid mixture.`

8. The process of producing substantially pure anhydrouis hydrouoric acid which comprises subjecting fluorspar tothe action of sulfuric acid and maintaining in the expelled gas stream a proportion o1' m* in excess of that which is capable of being condensed out in the form a Water solution of said acid, separating aqueous hydrouorie acid contained in the gas mixture thereby produced, by cooling, bringing the condensed liquid and the uncondensed HF gas to a temperature equilibrium, separating the liquid from the gas, refrlgerating the gas to reduce it to liquid form, passing the residual uncondensed gas through an absorbing ble of being condensed out in the form of a water solution of said acid, separating aqueous hydroiluoric acid contained in the gas mixture thereby produced, by cooling, bringing the condensed liquid and the uncondensed HF gas to a temperature equilibrium, separating the liquid from the gas, refrigerating the gasto reduce it to liquid form, passing the residual uncondensed gas ,through an absorbing medium, fractionating the absorbing medium, adding the liquid residue of.

the fractionating step to the absorbing medium, passing the residual gas not absorbed by the absorbing medium through a liquid capable of absorbing HF and adding the resultant dilute HF to the absorbing medium.

10. The process of producing substantially pure anhydrous hydroiluorlc acid which comprises subjecting uorspar to the action of a hot sulfuric acid under approximately anhydrous conditions so as to maintain in the discharging gas stream a proportion of HF in excess of that which is capable of being precipitated with the condensed moisture in the form of a saturated solution, subjecting the gas mixture so obtained to condensing conditions at a temperature slightly above the boiling point of HF at the pressure employed, conducting the gas and condensed liquid in co-currentrelationship until an approximate temperature equilibrium has been established between the condensed liquid and uncondensed HF gas, and then separating the liquid from. the gas.

11. The process of producing substantially pure anhydrous hydrouoric acid which comprises subjecting fluorspar to the action of hot sulfuric acid under approximately anhydrous conditions s as to maintain in the discharging l gas stream a proportion of HF in excess of that which is capable of being precipitated with the.

condensed moisture in the form of a saturated solution, subjecting the gas mixturedo condensing conditions by cooling the same to a temperature slightly above the boiling point of HF at the pressure employed, conducting the gas and liquid in co-current relation until an approx- Imate temperature equilibrium is established between the condensate and uncondensed HF, separating the liquid from the gas, removing suspended matter from the HF gas, andliquefying the anhydrous gas.

l2. The process of producing substantially pure anhydrous hydrouoric acid which comprises subjecting iuorspar to the action of hot sulfuric acid under approximately anhydrous conditions so as to main in the discharging gas stream a proportion of HIE' in excess of that which is capable of being precipitated with the condensed moisture in the fcrm of a saturated solution, subjecting the gas mixture so obtained to continuous cooling while conducting the uncondensed gas and condensed liquid in co-current relation until an approximate temperature equilibriurn between the uncondensed HF gas and condensate is established at a temperature slightly above the boiling point of HF at the pressure employed, separating the liquid from the gas, and then subjecting the gas to refrigeration in at least two stages of diminishing temperature, the last cooling stage being eiective to condense the anhydrous HF. i

13. The process of producing substantially pure anhydrous hydroiiuoric acid which comprises subjecting fiuorspar to the action of hot sulfuric acid .under approximately anhydrous conditions so as to maintain in the discharging gas stream a proportion of HF in excess of that which is capable of being precipitated with condensed moisture in the form of a saturated solution, subjecting the gas mixture so obtained to continuous cooling while maintaining the uncondensed HF in contact with the condensate until an approximate temperature equilibrium between the uncondensed HF and the condensate is established, at a temperature slightly above the boiling point of HF at the pressure employed,

isv

pure anhydrous hydroiiuorlc vsteld which comprises subjecting uorspar to the action of hot sulfuric acid imder roximately conditions so as to maintain in the a proportion of in ex which is capable of being precipitated with the condensed moisture in the form oi solution, leading the resultant gas' I into contact with a hydrouoric acid solution of lower temperature and thereby a c; tial of the fx" from the solution, coo

.er r :it to a tpeure which is ceove of producing substantially Y boiling point ot ,et the pr empl to cause precipitation of the water in the i'o oi a saturated solution of condu the gas and condensed liquid in co i i relation un tii an apprommate estab between the condte and uncon densed m, withdra and liqu the anhydrous gas so obtained, and n1-tig the liquid condensate into the path of further incoming volumes o f the hot gases produced by the treatment of hydrotiuoric acid with c acid.

15. A composition comprising the product resulting from the of approximately @M5 w `tinlly anhydrous iwdrouoric i und i parte of :n n im. 

